A Metabolomic Analysis of Omega-3 Fatty Acid-Mediated Attenuation of Western Diet-Induced Nonalcoholic Steatohepatitis in LDLR-/- Mice

Abstract

BackgroundNonalcoholic steatohepatitis (NASH) is a progressive form of nonalcoholic fatty liver disease and a risk factor for cirrhosis, hepatocellular carcinoma and liver failure. Previously, we reported that dietary docosahexaenoic acid (DHA, 22:6,n-3) was more effective than eicosapentaenoic acid (EPA, 20:5,n-3) at reversing western diet (WD) induced NASH in LDLR-/- mice.MethodsUsing livers from our previous study, we carried out a global non-targeted metabolomic approach to quantify diet-induced changes in hepatic metabolism. ResultsLivers from WD + olive oil (WD + O)-fed mice displayed histological and gene expression features consistent with NASH. The metabolomic analysis of 320 metabolites established that the WD and n-3 polyunsaturated fatty acid (PUFA) supplementation had broad effects on all major metabolic pathways. Livers from WD + O-fed mice were enriched in saturated (SFA) and monounsaturated fatty acids (MUFA), palmitoyl-sphingomyelin, cholesterol, n-6 PUFA, n-6 PUFA-containing phosphoglycerolipids, n-6 PUFA-derived oxidized lipids (12-HETE) and depleted of C20-22 n-3 PUFA-containing phosphoglycerolipids, C20-22 n-3 PUFA-derived oxidized lipids (18-HEPE, 17,18-DiHETE) and S-lactoylglutathione, a methylglyoxal detoxification product. WD + DHA was more effective than WD + EPA at attenuating WD + O-induced changes in NASH gene expression markers, n-6 PUFA and oxidized lipids, citrate and S-lactosyl glutathione. Diet-induced changes in hepatic MUFA and sphingolipid content were associated with changes in expression of enzymes involved in MUFA and sphingolipid synthesis. Changes in hepatic oxidized fatty acids and S-lactoylglutathione, however, correlated with hepatic n-3 and n-6 C20-22 PUFA content. Hepatic C20-22 n-3 PUFA content was inversely associated with hepatic α-tocopherol and ascorbate content and positively associated with urinary F2- and F3-isoprostanes, revealing diet effects on whole body oxidative stress. ConclusionDHA regulation of hepatic SFA, MUFA, PUFA, sphingomyelin, PUFA-derived oxidized lipids and S-lactoylglutathione may explain the protective effects of DHA against WD-induced NASH in LDLR-/- mice.

Docosahexaenoic acid attenuates Western diet-induced hepatic fibrosis in Ldlr mice by targeting the TGFβ-Smad3 pathway

“…Although the WD + D diet signifi cantly lowered TLR2 agonists in plasma, WD + E and WD + D failed to lower plasma TLR4 agonists. Failure of the 3 PUFA-containing diets to suppress TLR4 agonist is consistent with our previous fi nding, which showed that dietary 3 PUFAs do not attenuate WD-induced endotoxinemia ( 18 ). Hepatic fi brosis is also linked to products derived from adipose tissue and cells involved in innate immunity, including adipokines and cytokines, respectively ( 52,53 ).…”

“…We also reported that adding EPA (20:5, 3) or DHA (22:6, 3) to the WD affected diet-induced hepatic fi brosis. DHA was more effective than EPA at attenuating WD-induced hepatic fi brosis ( 17,18,28 ). Although EPA and DHA attenuated WD-induced dyslipidemia, neither EPA nor DHA affected WD-induced body weight, the percent of body fat, blood glucose, or plasma endotoxin.…”

“…Data were acquired using FACSCalibur (BD Biosciences), and data analyses were done using FCAP Array Software version 3.0 (BD Biosciences). Plasma for these assays was obtained from mice described previously ( 17,18 ).…”

“…We previously reported that Ldlr Ϫ / Ϫ mice fed a Western diet (WD) develop a NASH phenotype that recapitulates human NASH in obese patients, including obesity, hyperlipidemia, hyperglycemia, hepatic damage, hepatosteatosis, induction of multiple markers of infl ammation, oxidative stress, and fi brosis ( 17,18 ). The WD is moderately high in saturated fat and trans-fat (43% total calories), and simple sugar (30% total calories), and cholesterol (1.5 g%) and refl ects a modern, but unhealthy, diet ( 19 ).…”

“…Although EPA and DHA attenuated WD-induced dyslipidemia, neither EPA nor DHA affected WD-induced body weight, the percent of body fat, blood glucose, or plasma endotoxin. The effect of C 20-22 3 PUFA on hepatic fi brosis was established by histology and quantifying the expression of fi brosis markers (i.e., Col1A1 and TIMP1) ( 17,18 ). DHA and EPA are known to attenuate infl ammation, decrease fatty acid synthesis, and increase fatty acid oxidation ( 29 ).…”